Keep AC on or off when not at home

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My thermostat went bonkers last winter and my landlord had me call NV Energy and put in a smart thermostat. I actually like it and it has saved me on my bill. I set it for 74 from 8a- 6p, 72 6p- 10p, and 70 from 10p- 8am. My desk and computer are in my bedroom which of course is the hottest in the house as it is south facing. I work PT in the evenings from home so I like to cool it down.

When the guy installed the thermostat he said the temp reading is the temp right here in the hall so other rooms can be cooler or warmer. My bedroom is at least 5-7 degrees warmer. Last summer before the thermostat, my bills came close to $400. This summer, my equal pay was $299 but I never reached that and most were less than $200. The new equal pay is $156 starting in September.

I have an older home and pretty sure insulation is not as good as the newer built homes. If I was leaving for an extended period of time, say more than 2 days, I would up it to maybe 78-80. I also have 2 senior dogs so if they were home I probably would not go above 75. If they were boarded and the house was empty- maybe 80.

Just for the sake of debate, I just ran an amortization in a spreadsheet on my other screen...

For a $16K, 15 SEER variable unite over 15 years, with an average utility cost of %60 of a single stage rated at $60/mth(I base this on what my smart meter says my unit costs me) leave you at $36/mth average over the year....

after 13 years of service it costs you a total of $16468.

A single stage, same rating, costing $6700 to install (thats what mine cost) with an average of $60/mth over the year(thats what mine costs)...

after 13 years of service it costs you a total of $7480.

Well, that's quite a difference.

Anyways, I'm not debating that advancement of that technology, but if it costs you more in the long run to have it, why run it?

Those economics are pretty compelling.

A couple of thoughts. While the average life of an AC system may be 13 years (I'll take your word for it), that doesn't mean you replace the entire system when it breaks. These systems are designed to be repaired. The major components include circuit boards with relays (replaceable), condenser motor (replaceable), evaporator (replaceable -- I think), compressor motor (replaceable), blower motor (replaceable) thermostat (replaceable) and some other things an HVAC engineer would identify in the image below. Many of these things can be replaced in the same sense as replacing a major component on an automobile.

For example, the start-up capacitor on the condenser fan failed on one of my units. The symptom was warm air blowing from the registers inside the house, and the outside condenser fan didn't start up. However, if I poked a yardstick through the top and gave the blades a shove, then the fan would spin up to speed and I would get cold air blowing through the registers inside the house. I didn't even bother to pull out my digital multimeter. I think I bought a replacement capacitor locally for less than $30 and installed it myself and life is good. I did watch a couple of Youtube videos before doing the actual replacement.

I have several units, so decided to check my other units for the same thing. So, while standing on the side of the house by the condenser fans, I logged in and one by one started each of the AC units. It turns out one of them was slow to spin the fan up to speed, so I went online (less expensive then locally) and bought a replacement for about $18 IIRC, shipping included. It took a week to arrive, but that's OK. I installed it, and once again, that unit spun up to speed normally rather than slowly.

In a different house, I had an HVAC tech replace a circuit board. Watching him, I'm confident I could do that myself should the need arise.

Of course, the actual refrigerant service must be done by a licensed HVAC tech.

Let's say the lives of those two parallel systems can be extended to 30 years via repair/maintenance. I suspect the economics don't change - the less expensive unit is still the one to buy.

****

The other thing is that money isn't everything. I don't merely look at the electrical efficiency when I make a decision. I also think about comfort. I suspect the variable speed system would provide a more comfortable living environment, as it is always circulating cold air, rather than start/stop/start/stop. That's just a guess.

I keep it at 78-80 when home. 85-86 when I leave for work. I have dogs in a crate that I put a fan near. 85 is cool enough if you come from the outside on a 105 degree day. If you have no pets and go on vaca I’d prob turn it off. Or put it at 90. If you have plants they will die if the AC is off.

My thermostat went bonkers last winter and my landlord had me call NV Energy and put in a smart thermostat. I actually like it and it has saved me on my bill. I set it for 74 from 8a- 6p, 72 6p- 10p, and 70 from 10p- 8am. My desk and computer are in my bedroom which of course is the hottest in the house as it is south facing. I work PT in the evenings from home so I like to cool it down.

When the guy installed the thermostat he said the temp reading is the temp right here in the hall so other rooms can be cooler or warmer. My bedroom is at least 5-7 degrees warmer. Last summer before the thermostat, my bills came close to $400. This summer, my equal pay was $299 but I never reached that and most were less than $200. The new equal pay is $156 starting in September.

I have an older home and pretty sure insulation is not as good as the newer built homes. If I was leaving for an extended period of time, say more than 2 days, I would up it to maybe 78-80. I also have 2 senior dogs so if they were home I probably would not go above 75. If they were boarded and the house was empty- maybe 80.

That's what is so cool - no pun intended - about thermostats like the Nest. You can put temperature sensors in multiple rooms and tell it which sensor to read from.

Definitely people are repairing things like capacitors, contactors, and blower fans. I've had half a dozen friends and family had to replace their AC units this season. Empirically, it seems once there is any sort of issue with the actual refrigerant system (compressor failure, condenser leak, etc.) and especially after the system is 10+ years old, the technicians tell you to just replace the system. A compressor swap including refrigerant recharge is probably in the cost range of $2000-$2500 would be my guess. The techs and HVAC companies don't really want to do that type of work, they'd much rather just swap a system. A more definitive outcome, more profit, and higher chance of a happy customer. So they steer (heavily) in that direction.

Bottom line, I don't see many people stretching the life of their AC units with repairs.

15-20 years seems to be a pretty typical lifespan. Probably replacing a contactor and capacitor along the way.

Quote:

Originally Posted by RationalExpectations

For example, the start-up capacitor on the condenser fan failed on one of my units. The symptom was warm air blowing from the registers inside the house, and the outside condenser fan didn't start up. However, if I poked a yardstick through the top and gave the blades a shove, then the fan would spin up to speed and I would get cold air blowing through the registers inside the house. I didn't even bother to pull out my digital multimeter. I think I bought a replacement capacitor locally for less than $30 and installed it myself and life is good. I did watch a couple of Youtube videos before doing the actual replacement.

I have several units, so decided to check my other units for the same thing. So, while standing on the side of the house by the condenser fans, I logged in and one by one started each of the AC units. It turns out one of them was slow to spin the fan up to speed, so I went online (less expensive then locally) and bought a replacement for about $18 IIRC, shipping included. It took a week to arrive, but that's OK. I installed it, and once again, that unit spun up to speed normally rather than slowly.

In a different house, I had an HVAC tech replace a circuit board. Watching him, I'm confident I could do that myself should the need arise.

Of course, the actual refrigerant service must be done by a licensed HVAC tech.

Let's say the lives of those two parallel systems can be extended to 30 years via repair/maintenance. I suspect the economics don't change - the less expensive unit is still the one to buy.

A couple of thoughts. While the average life of an AC system may be 13 years (I'll take your word for it), that doesn't mean you replace the entire system when it breaks. These systems are designed to be repaired. The major components include circuit boards with relays (replaceable), condenser motor (replaceable), evaporator (replaceable -- I think), compressor motor (replaceable), blower motor (replaceable) thermostat (replaceable) and some other things an HVAC engineer would identify in the image below. Many of these things can be replaced in the same sense as replacing a major component on an automobile.

For example, the start-up capacitor on the condenser fan failed on one of my units. The symptom was warm air blowing from the registers inside the house, and the outside condenser fan didn't start up. However, if I poked a yardstick through the top and gave the blades a shove, then the fan would spin up to speed and I would get cold air blowing through the registers inside the house. I didn't even bother to pull out my digital multimeter. I think I bought a replacement capacitor locally for less than $30 and installed it myself and life is good. I did watch a couple of Youtube videos before doing the actual replacement.

I have several units, so decided to check my other units for the same thing. So, while standing on the side of the house by the condenser fans, I logged in and one by one started each of the AC units. It turns out one of them was slow to spin the fan up to speed, so I went online (less expensive then locally) and bought a replacement for about $18 IIRC, shipping included. It took a week to arrive, but that's OK. I installed it, and once again, that unit spun up to speed normally rather than slowly.

In a different house, I had an HVAC tech replace a circuit board. Watching him, I'm confident I could do that myself should the need arise.

Of course, the actual refrigerant service must be done by a licensed HVAC tech.

Let's say the lives of those two parallel systems can be extended to 30 years via repair/maintenance. I suspect the economics don't change - the less expensive unit is still the one to buy.

****

The other thing is that money isn't everything. I don't merely look at the electrical efficiency when I make a decision. I also think about comfort. I suspect the variable speed system would provide a more comfortable living environment, as it is always circulating cold air, rather than start/stop/start/stop. That's just a guess.

Yeah, the temp is more consistent, same with the inverter refrigerators that use 40% less electric. Food stays fresher longer.

Yeah, the temp is more consistent, same with the inverter refrigerators that use 40% less electric. Food stays fresher longer.

Thatís exactly right. Iíve had both and I canít tolerate the on / off nonsense. It goes from cold to hot to cold to hot never reaching anything approaching a good temperature. A variable unit will always leave you comfortable and use exactly the energy it needs to use. Iím not fretting over money whatsoever when it comes to my personal comfort - Iíll spend the money. This isnít buying a Ferrari ďfor fun,Ē itís your entire life inside of your home and effects every second of that. Given Iím home most of the time, thatís ďlifeĒ itself. Worth the money, Iíd say.

And LOL at 85 degrees being comfortable inside. Get. Real. Even with a killer ceiling fan 85 is WAY too hot for inside!

Thatís exactly right. Iíve had both and I canít tolerate the on / off nonsense. It goes from cold to hot to cold to hot never reaching anything approaching a good temperature. A variable unit will always leave you comfortable and use exactly the energy it needs to use. Iím not fretting over money whatsoever when it comes to my personal comfort - Iíll spend the money. This isnít buying a Ferrari ďfor fun,Ē itís your entire life inside of your home and effects every second of that. Given Iím home most of the time, thatís ďlifeĒ itself. Worth the money, Iíd say.

And LOL at 85 degrees being comfortable inside. Get. Real. Even with a killer ceiling fan 85 is WAY too hot for inside!

I think if you re-read it, they were stating it's fine to walk into from after a day of work- they would be turning it down.

I’m on the time of use program. I set the thermostat at 72 and turn off the system at 2pm. Turn it back on at 7pm. At 7 pm the house is at 78. Electric bill for 3400 sq ft house July about $200.

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